We have 1) designed an "ideal" immunochemical reagent based on our best knowledge of biocompatible materials and immunochemistry; 2) synthesized uniform polymeric spheres of sizes from 300 A to 10,000 A in diameter; 3) covalently bonded antibodies and fluroescent dyes to the spheres; and 4) demonstrated the feasibility of their use as tagged markers for studies of cell surface antigens. We propose to extend these studies further. Several types of immunochemical reagents are proposed. Some will carry radioactive tags for use in radioimmune assays and radioautography. Some will also carry various types of fluorescent tags which will serve as visual markers for the study of cell surfaces in the scanning electron microscope. We also propose to continue to develop further solid phase immunological approaches for the isolation of cells and cell memebranes. Finally, we plan to explore the effectiveness of these new reagents in studies of the nature, location and distribution of the interesting antigenic sites known to be present on the surface of immune related murine tumor cell lines.